This program will continue to develop photoradiation therapy (hematoporphyrin derivative, Hpd and visible light) as an effective therapy for various solid tumors in man. At the same time, we continue to study mechanisms relating to tumor specificity of Hpd, mode of cellular inactivation, repair processes, oxygen effect, light distribution in tissue, especially using a fiber-optic delivery light from a dye-laser directly into tissue. Studies of this type require exchange and binding experiments of Hpd for various tissue, tissue culture studies, autoradiography, electron microscopic methods, optical techniques and numerous in vivo systems. Intra-operative clinical studies are planned to evaluate photoradiation for control of tumors of the bone, esophagus, gastric organs and colo-rectal tumors. These procedures require interstitial implant of the light delivery fiber of the dye-lasar. Also, a detailed study of breast carcinoma metastatic to soft tissue is being undertaken in order to properly evaluate several parameters in photoradiation therapy.